Mechanisms and models of iridium anomaly shape across the Cretaceous-Paleogene boundary

作者：Hull Pincelli M^*; Franks Peter J S; Norris Richard D

来源：Earth and Planetary Science Letters, 2011, 301(1-2): 98-106.

DOI：10.1016/j.epsl.2010.10.031

• KIT boundary
• impact ejecta
• bioturbation
• PGE
• advection-diffusion model
• fossil record preservation

The interpretation of the Cretaceous-Paleogene (K-Pg) iridium anomaly - and other impact ejecta - as the result of a single, large asteroid impact has been the subject of much debate, in part due to the distribution of impact markers beyond the narrow confines of the K-Pg boundary sedimentary layer. Here, we revisit the hypothesized processes leading to the shape of K-Pg iridium profiles including geochemical remobilization and/or diffusion, prolonged deposition, volcanism, multiple impacts, and sediment mixing. Using evidence from the literature and modeling of one North Pacific site, we find that sediment mixing of a single impact event provides the most parsimonious mechanism for iridium profile shape in open ocean oxic sediments, while the increase in background iridium bracketing the boundary likely has a volcanic origin. In some past studies, a sediment mixing mechanism for iridium profile shape was ruled out based on an overly simplified set of expectations for the effect of sediment mixing on markers of geologically instantaneous events. Thus, we introduce and use a Lagrangian sediment mixing model to illustrate the theoretical effects of mixing on records of rapid events. The sediment mixing origin for iridium anomaly shape, the correspondence in mixing extent between iridium and microfossils, and the fit of sediment mixing models to an empirical iridium profile indicate that iridium may provide a better tracer of mixing than previously proposed K-Pg mixing tracers such as Ni-spinels.

• 出版日期2011-1-3